Circuit arrangements with a power input and at least one power supply unit for generating a DC voltage for operating an electronic device are widely known. In particular, an ever larger number of devices in communications and entertainment electronics require at least one power supply unit to generate a rectified low voltage in the range of 1-24 V from the ordinary 230 VAC mains voltage. The power supply units that are used in that instance must satisfy different, to some extent contradictory, requirements.
First, the power supply unit must be electronically switched on and off, i.e., without actuating a mechanical switch. This has the advantage, among others, that it is possible to do without high-voltage resistant, relatively expensive power switches and expensive cabling and electromagnetic shielding in a device housing. In addition, such a device can be switched on via a timer or other electronic controller.
Second, the power supply unit and the device connected to it should consume as little power from the power grid as possible in a shut-off or standby state to avoid unnecessary use of energy. Currently available devices generally consume a few watts of power in so-called “stand-by” mode, which leads to unnecessary emissions of greenhouse gases for power generation.
Third, efficiency of the power supply unit must be as high as possible, and the noise power fed from it into the mains network must be as low as possible. For this purpose, the power supply unit must comply with increasingly strict requirements of regulatory agencies and power grid operators.
Switched-mode power supply units with upstream network filters and circuits for correcting the power factor are generally used to supply relatively large and rapidly varying loads. A clock frequency or a duty factor of a control signal is generally used to control the load. A disadvantage of such circuits is that they have a relatively high power loss, particularly in standby mode, an operating mode with a very low output power.
It could therefore be helpful to provide a circuit arrangement that satisfies the requirements mentioned above particularly well, in particular, a circuit arrangement and an operating method for controlling a power input circuit whose power consumption from a power grid in the energy-saving state is minimal are to be described. It could also be helpful to provide, in the energy-saving state, an arrangement that preferably does not consume any electrical energy from the power grid at all. In addition, the circuit arrangement should, to the extent possible, contain no mechanical or electromechanical switching elements and be constructed relatively simply.